What Is Oxytocin?

Overview

Definition of oxytocin

The term "oxytocin" refers to a hormone and a neurotransmitter your body naturally produces.¹ Hormones play an integral role in your body by being released from the endocrine system and acting as messengers that travel within your bloodstream. Oxytocin is also considered to be a neurotransmitter, allowing communication between the brain cells (neurons). 

Importance in human biology

Oxytocin has many benefits for the body, especially during childbirth, milk production, and ejection during breastfeeding. The hormone is also important for maternal behaviour and bonding with others. Oxytocin’s function extends to your social behaviours and your overall well-being.²

Structure and function of oxytocin

Chemical structure of oxytocin     

Oxytocin consists of nine amino acids, which are the fundamental building blocks of proteins and peptides.¹ Proteins and peptides play a vital role in our bodies, for example, enabling chemical reactions and communication between the cells. Oxytocin is considered to be a peptide, as it’s a short structure made of amino acids in the following arrangement: cysteine, tyrosine, isoleucine, glutamine, asparagine, cysteine, proline, leucine and glycine, followed by a chemical group known as the amide group.³ 

The chemical structure of oxytocin. Oxytocin promotes a sense of safety and bonding between individuals. Source: Wikimedia Commons. 

https://commons.wikimedia.org/wiki/File:Oxytocin_hormone_15.tif

Role as a hormone

Oxytocin has diverse roles in your body. When it comes to individuals assigned female at birth (AFAB), oxytocin has a role in female reproduction. This includes a role in contractions of the uterus (womb) during childbirth and milk ejection when breastfeeding.⁴ When it comes to individuals assigned male at birth (AMAB), oxytocin has a role in ejaculation.⁵  Non-reproductive roles of oxytocin include facilitating social behaviours such as trust, human bonding, and our attachment to others.⁴

How is oxytocin made in the brain?

Oxytocin is made in the hypothalamus in your brain, which is a centre maintaining homeostasis, an internal balance of the processes happening inside your body. It keeps things such as your temperature, oxygen levels, and blood sugar in check. 

The hypothalamus is labelled on the brain MRI scan (on the left). The hypothalamus sits on top of the pituitary gland (on the right) and instructs it to release oxytocin when needed. Created using Canva and Wikimedia Commons by Antonina Swierkowska. 

https://commons.wikimedia.org/wiki/File:Hypothalamus.jpg

https://commons.wikimedia.org/wiki/File:201405_pituitary_gland.png

The hypothalamus makes oxytocin in its specific areas called paraventricular and supraoptic nuclei.⁶ But where is the oxytocin stored and released? Oxytocin is stored and released from the pituitary gland in your brain, as instructed by the hypothalamus. The pituitary gland is an endocrine gland, which is very small, approximately the size of a pea. Your pituitary gland consists of two lobes called the anterior (front part), and the posterior lobes (back part). These two structures do not communicate or interact with each other, but both release various hormones, which have different effects on your body. Oxytocin is only released from the posterior pituitary gland.⁷ When the neurons are stimulated enough, the brain releases oxytocin from the pituitary gland into the blood. 

What are the biological effects of oxytocin?

Non-reproductive functions

Maternal bonding

Animal studies set the scene for investigating the maternal bonding role of oxytocin in humans, with oxytocin being shown to induce maternal behaviour in animals. In humans, higher oxytocin levels in the mother before, during or immediately after giving birth have been associated with more infant and mother bonding.⁸

Pair bonding

In your blood plasma, the amount of oxytocin increases when you form new romantic relationships with others, suggesting that oxytocin has a role in the formation of romantic bonds, especially at their initial stages.⁸

Influence on emotional, mental and social behaviour

The effect of oxytocin on emotional behaviour has been studied in male mice. To work, oxytocin needs to bind to oxytocin receptors to have a biological effect on the body. In mice that do not have oxytocin receptors, there is a rise in depressive-like symptoms. The opposite was true for mice with oxytocin receptors, in which an antidepressant-like effect was observed. Similarly, when looking at humans, as blood plasma oxytocin levels in the body start to decrease, there is an increase in the development of major depressive disorders.⁶

Interestingly, childhood trauma has also been shown to negatively impact the oxytocin system within the human body, causing children to develop insecure attachment styles to others and mental health conditions, highlighting the importance of oxytocin in children’s emotional development.⁸

The social role of oxytocin has also been investigated in rats, another rodent model used in health research. Administering a high dosage of the drug phencyclidine caused social interaction deficits in rats. When these rats were then treated with oxytocin, it reversed any social interaction deficits that the rats were experiencing. Oxytocin has also been shown to increase the amount of time that rats spend socially interacting with one another, indicating that oxytocin has a role in social interactions and social bonds.⁹  However, it is worth noting that as much as research on rodent models, such as mice and rats, is important, it does not automatically give us answers to what happens in humans. We need research validating the results from mice to gain a full understanding of the biological processes in the human body. When it comes to oxytocin, besides having a social role in animals, it also has a role in humans, aiding in your social life and interactions with others.¹⁰

Trust and empathy

Having more oxytocin in your body has been consistently associated with having a higher level of trust for others and more empathy for other’s situations. This is because more oxytocin reduces the activation of a part of your brain known as the amygdala, which has a role in our fear response.¹⁰

Stress reduction

The hormone oxytocin plays a role in reducing stress by bringing out anti-stress effects, such as reducing your blood pressure, which increases when you find yourself in a high-stress situation. Oxytocin also reduces the amount of cortisol, a hormone, which travels around your body and elicits the stress response, which in everyday terms is known as the fight or flight response.¹¹

Reproductive functions

Stimulating uterine contractions

Oxytocin has a role in stimulating uterine contractions during birth, where the uterus (the womb) contracts to help push out the baby during birth. As the baby’s head pushes against its mother’s cervix, this sends a signal to the posterior pituitary gland in the brain to secrete more oxytocin into the blood, which causes uterine contractions. The uterine contractions will continue to trigger more oxytocin release from the pituitary gland, causing more uterine contractions. This cycle will continue until the baby is delivered.¹²

Facilitating milk ejection (letdown reflex)

The reproductive role of oxytocin extends to milk ejection when a mother is breastfeeding her baby. Oxytocin causes the alveolar ducts of a female’s breasts to contract. The contractions cause the milk to be ejected into larger ducts, ready to be ejected from the breast. When a baby feeds on its mother’s breast, this sends signals to the brain to secrete oxytocin, which in turn causes more milk ejection from the breast.¹²

Oxytocin and stress

In humans, oxytocin has been shown to counteract the stress response by reducing the activity of the so-called hypothalamic-pituitary-adrenal axis (HPA).¹³ The HPA axis is responsible for the body’s adrenal glands (glands on top of the kidneys) releasing cortisol, known as the stress hormone, which mediates the fight or flight stress response. 

Oxytocin in medical applications

How can oxytocin be used to induce labour?

Oxytocin can be used to start labour for AFABs who have inactive uteri. Therefore, their uterus does not contract to start labour, meaning that the baby cannot be delivered naturally.¹² Oxytocin can also be used to speed up slow labour, and after administration intravenously (via a drip in the arm), you can expect the effects of the oxytocin to show after approximately 30 minutes.¹⁴

How can oxytocin help manage a postpartum haemorrhage?

Oxytocin is given after a postpartum haemorrhage (heavy bleeding after birth), as it causes the uterus to contract, as it does during birth, helping to prevent any excessive bleeding. Oxytocin is more effective at preventing this when it is administered by injection into your vein rather than your muscle.¹⁵

Does oxytocin have a potential role in treating autism and anxiety disorders?

Studies investigating oxytocin have shown that less oxytocin is common in those with anxiety disorders, suggesting that increasing oxytocin levels within the body may aid in the treatment of anxiety disorders.¹⁰ In addition, whilst less oxytocin is not thought to cause autism, giving children oxytocin seems to aid in their development of social skills.¹² This makes the oxytocin system in the brain a potential target for treating psychiatric conditions, anxiety, autism and postpartum depression.¹⁰

Oxytocin and mental health

Influence on mental well-being

Low oxytocin levels in the body have been associated with mental health disorders, such as anxiety and depression.¹⁰ Oxytocin is typically known as a ‘feel good hormone’, helping you feel happier and at ease and ultimately aiding your overall mental well-being. Oxytocin is released from the pituitary gland when you engage in social bonding behaviours, such as openly communicating with others in your life, when you pet animals, and when you listen to music. ¹⁶

Links to mental health conditions and autism spectrum disorders

Oxytocin is the bonding hormone and helps you socially bond with others. However, low oxytocin may be part of the explanation as to why individuals with autism spectrum disorders, such as Asperger’s syndrome, have poor social skills.¹⁷

Low oxytocin levels are also reported in individuals with anxiety or depression, highlighting the importance of this hormone in your overall mental well-being and health.¹⁰

Summary

• Oxytocin is a hormone and neurotransmitter produced by your body
• Oxytocin is commonly termed the ‘bonding hormone’ and has a role in your feelings of trust and attachment to others, as well as your emotional regulation
• Oxytocin is made in the hypothalamus in your brain and released subsequently from the posterior pituitary gland
• This hormone has a role in reproduction, especially concerning uterine contractions during childbirth
• Oxytocin has a role in breastfeeding and milk ejection from a mother’s breast, as well as maternal behaviour 
• Oxytocin can aid in counteracting the stress response caused by the stress hormone cortisol
• Oxytocin can be used to aid in conditions such as a postpartum haemorrhage and to induce labour
• Low oxytocin levels are associated with poor social skills and social bonding, which is seen in individuals with autism spectrum disorders.
• Low oxytocin is also observed in those who have anxiety and depression